How come my check engine light will not come on when I have a problem. It didn't come on the two seperate times I left the gas cap off. It didn't come on When my TCL quit working or when the tranny completely died a short time later. It never came on a little bit ago the jeep would sputter in the rain and once it about died on me going 35 mph but no CEL (that last problem was fixed by a new cap, rotor, and upstr. oxygen sensor). I guess my CEL can work because it stayed on for a day when I had my fuel pump replaced. Any body else ever have this problem?

Well I was thinking that the engine about dying while going down the road would have sent some sort of code. Maybe I shuld purposly unplug something and see if it throws a CEL. also I always thought that the gas cap being loose (or off) would set off a code.

If your Jeep is a newer one ('00 or '01 or newer I've heard), trun the key ON-OFF-ON three times within 5 seconds to display the DTC on the odometer. If the CEL bulb is blown, there should be codes stored and will show up using this test. If no codes display, then bulb probably isn't blown.

Try unpluging the Engine Coolant Temperature sensor on the thermostat housing and crank it. I forgot to reconnect this the other day when I was changing my thermostat and the CEL came on immediately. Don't leave it off for a long time, just long enough to check you CEL.

There are certain codes that are not considered critical. For those, the CEL does not illuminate. It is assumed that when you service the vehicle, you will check the codes and repair those items. It is only items that cause serious emission problems, or problems with the operation of the vehicle that trip the CEL. Repair manuals talk about the specifics, and code charts show which are which.

I know that the light isn't burned out since it comes on when I start it. When the jeep almost died in the rain I did the code check thing and it worked but didn't get any codes. Brown dog might be right about any of the codes not being critical.